Silicon nitride films are known to exhibit excellent barrier properties and an excellent oxidation resistance and are used, for example, as etch-stop layers, barrier layers, gate insulation layers, gate spacers, advanced gate dielectric, ONO stacks or the like in the manufacture of semi-conductor devices.
The main technologies in use at the present time for the formation of thin silicon nitride oroxynitride films are plasma-enhanced CVD (PECVD) and low-pressure CVD (LPCVD).
In PECVD, a silicon source (typically a silane) and a nitrogen source (such as, for example, ammonia but also nitrogen) are introduced between a pair of parallel-plate electrodes and radio-frequency energy is applied between the two electrodes at low temperatures (about 300° C.) and intermediate pressures (0.1 to 5 Torr or 1 to 630 Pa) in order to generate a plasma from the silicon source and nitrogen source. Active silicon species and active nitrogen species in the generated plasma react with each other to produce a silicon nitride film.
The silicon nitride films produced by PECVD generally do not have a stoichiometric composition and are also hydrogen rich. As a result, these silicon nitride films have a low film density and a high etch rate and are of poor quality. They are often referred to as SiNH, since they contain up to 30% H atomic. However, PECVD is not preferred for front end applications (FEOL) because of the damages that may be generated by the plasma at the semi-conductors surface.
Thermal LPCVD which does not employ a plasma, is used to deposit high-quality silicon nitride films. LPCVD as it is currently practiced uses low pressures (0.1 to 2 Torr) and high temperatures (750-900° C.) and produces silicon nitride or oxynitride films of a quality superior to that of the corresponding films produced by PECVD. Silicon nitride films made by using LPCVD technology, are generally obtained by the reaction of dichlorosilane (DCS) and ammonia gas. However, the existing LPCVD technology requires fairly high temperatures in order to obtain acceptable deposition (film formation) rates (≧10 Å/minute) for silicon nitride films. For example, temperatures of 750 to 800° C. are typically used for the reaction of DCS and ammonia. In addition, the reaction of DCS and ammonia produces large amounts of ammonium chloride, which can accumulate in and clog the exhaust piping system of the CVD reaction apparatus.
A number of silicon nitride precursors have been introduced for the purpose of obtaining satisfactory silicon nitride film deposition rates at low temperatures. Hexachlorodisilane (HCDS) is one example of such precursors. HCDS produces SiCl2 at relatively low temperatures by the reaction Si2Cl6→SiCl2+SiCl4 and this SiCl2 reacts effectively with ammonia. The use of HCDS can provide silicon nitride film deposition at film formation rates of approximately 10 Å/minute at 600° C.
Another example of a silicon nitride precursor is the bis(tert-butylamino)silane (BTBAS) described in U.S. Pat. No. 5,874,368. BTBAS enables the deposition of silicon nitride films at a film formation rate of approximately 10 Å/minute at 600° C.
While both HCDS and BTBAS can achieve film formation rates of approximately 10 Å/minute at 600° C., this performance level also means that commercially acceptable film formation rates will not be obtained at temperatures lower than 550° C. Furthermore, these precursors have also the following drawbacks:
HCDS, being a completely chlorinated disilane, has a high chlorine content, and the Si—Cl bond is also very strong. As a consequence, the chlorine content in the resulting silicon nitride film will increase as the reaction temperature declines, and it has been found that the chlorine content can be as high as about 2% (atom based) in a film obtained at a 600° C. reaction temperature. In addition, the use of HCDS also leads to the production of large amounts of ammonium chloride just as in the case of DCS.
BTBAS has an activation energy of 56 kcal/mole, with the result that its silicon nitride film formation rate declines drastically when the reaction temperature is reduced. It is estimated that its film formation rate drops to a quite small 3 Å/minute at a reaction temperature of 550° C.
It is also known to use tetrakis(ethylamino) silane (“TEAS”) as a Si precursor to manufacture films at a similar growth rate than the grow rate obtained with BTBAS but with different film properties.
The same problems appear when the aforementioned prior art precursors are used to produce silicon oxynitride films, which have the same physical properties and applications as silicon nitride films.
It is also known from PCT WO03/045959 et PCT WO03/046253 that hexathylaminodisilane which provide for better Si precursors to manufacture films at growth rates of 10 Å or more at temperatures substancially lower than HCDS or BTAS.
The issue addressed by this invention, therefore, is to provide a method for the production of silicon nitride and silicon oxynitride films by CVD technology, wherein said method provides acceptable film formation rates at lower temperatures and is not accompanied by the production of large amounts of ammonium chloride.